In spring 2018, cybersecurity researcher Takeshi Sugawara found that point a laser at an iPad’s Microphone converted the light into sound. Then, according to Wired, he discovered the same technique could hack smart home devices like the Amazon Echo and Google Home.
Sugawara pointed a high-powered laser at the microphone of his iPad—all inside of a black metal box, to avoid burning or blinding anyone—and had Fu put on a pair of earbuds to listen to the sound the iPad’s mic picked up. As Sugawara varied the laser’s intensity over time in the shape of a sine wave, fluctuating at about 1,000 times a second, Fu picked up a distinct high-pitched tone. The iPad’s microphone had inexplicably converted the laser’s light into an electrical signal, just as it would with sound. Six months later Sugawara—visiting from the Tokyo-based University of Electro-Communications—along with Fu and a group of University of Michigan researchers have honed that curious photoacoustic quirk into something far more disturbing.